According to Apple, the slowing of older models is done only to “prolong the life” of the devices, to compensate for the declining performance of older batteries over time.

The current controversy was sparked when one user posted performance tests on Reddit that showed the performance of their iPhone 6S had slowed over time, speeding up only when the battery had been replaced. The tech website Geekbench then analyzed a range of iPhones running various operating systems, finding that some had seen their performance deliberately slowed.

In response, Apple admitted to slowing older models, saying:

“Lithium-ion batteries become less capable of supplying peak current demands when in cold conditions, have a low battery charge or as they age over time, which can result in the device unexpectedly shutting down to protect its electronic components.”

“Last year, we released a feature for iPhone 6, iPhone 6s and iPhone SE to smooth out the instantaneous peaks only when needed to prevent the device from unexpectedly shutting down during these conditions.”

They added that they plan to bring the feature to iPhone 7 models running iOS 11.2, saying it allows the company to “deliver the best experience for customers.”

Tech bloggers and customers still criticized Apple, however, for not informing customers their phones were being slowed. And now, the company is facing lawsuits.

According to a statement from Sulaiman Law Group’s James Vlahakis, who represents the plaintiffs in the Chicago lawsuit:

“Apple’s failure to inform consumers these updates would wreak havoc on the phone’s performance is being deemed purposeful, and if proven, constitutes the unlawful and decisive withholding of material information.”

He said the move would constitute a “direct violation” of consumer-fraud law in Illinois, Indiana, and North Carolina, where the plaintiffs reside.

The phones can be sped up again with the purchase of a new battery, which costs 79 dollars in the US.